66661817 has 2 divisors, whose sum is σ = 66661818. Its totient is φ = 66661816.

The previous prime is 66661813. The next prime is 66661831. The reversal of 66661817 is 71816666.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 63936016 + 2725801 = 7996^2 + 1651^2 .

It is a cyclic number.

It is not a de Polignac number, because 66661817 - 2² = 66661813 is a prime.

It is a super-3 number, since 3×66661817³ (a number of 24 digits) contains 333 as substring.

It is not a weakly prime, because it can be changed into another prime (66661813) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33330908 + 33330909.

It is an arithmetic number, because the mean of its divisors is an integer number (33330909).

Almost surely, 2^66661817 is an apocalyptic number.

It is an amenable number.

66661817 is a deficient number, since it is larger than the sum of its proper divisors (1).

66661817 is an equidigital number, since it uses as much as digits as its factorization.

66661817 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 72576, while the sum is 41.

The square root of 66661817 is about 8164.6688236572. The cubic root of 66661817 is about 405.4703005824.

The spelling of 66661817 in words is "sixty-six million, six hundred sixty-one thousand, eight hundred seventeen".